Recently, horizontal wells are preferred over vertical wells due to their larger reserve exposure and higher production rate, which together lead to better economic reward and possible higher recovery of the natural resources. In some cases, heavy oil is effectively produced through injection of a hot fluid, such as steam, to reduce viscosity of the heavy oil and to help drive the heavy oil to a nearby production well.
A proven and practical technology for in-situ operations to produce the larger reserves of heavy oil, such as Canadian bitumen from oilsands, is steam assisted gravity drainage (SAGD). Steam is injected downhole to reduce the viscosity and mobilize heavy oil for recovery at a production well. Downhole pumps, that operate at steam temperature, at large flow rates and at low bottom hole pressures, pump the heavy oil through the production well to the surface. Typical performance characteristics of a suitable SAGD pump can include: fluid lifting rates greater than 1200 m3/d, operating temperatures greater than 250° C., capability of landing at true 90 degrees horizontal sections, a high tolerance of well bore trajectory for running into hole and operation, controllable, stable and low downhole pressure for less back pressure to reservoir, less reservoir sand interruption, a high tolerance of vapor content especially when hot fluid changes phase, a long service life and reasonable installation costs.
To date, production capacity of about 1000 m3/d from a hot SAGD well has been constrained by the capacity of downhole pumps, despite higher maximum reservoir delivery capability.
Further, producing heated heavy oil or bitumen from downhole has been very challenging. The industry in general has not been satisfied with the available hot fluid downhole pumps, in particular for large rate SAGD wells.
Accordingly, attempts to meet the horizontal well and SAGD production have been mainly limited to modification of existing downhole pumps, such as electrical submersible pump (ESP), namely modified for higher temperature application. Other pumps which have been tried include metal on metal progressive cavity pumps (PCP).
Some producers are still using large sucker rod beam pumps, with the increased risks including jeopardizing the productivity and steam chamber growth in exchange for longer pump run life and lower cost when compared to the more expensive high temperature ESP. However, sucker rod pumps which use surface drive reciprocating pumps and PCP's are often challenged by mechanical stress fatigue and other mechanical issues when used in horizontal wells, particularly in changes in well direction.
Other attempts and trials include the use of gear pumps, twin screw pumps and hydraulic gas pumps which are still under development.
U.S. Pat. No. 6,973,973 to Weatherford discloses a hydraulic gas pump (HGP) which utilizes natural gas as a power gas drive for pushing liquid from a chamber landed in horizontal well. After the gas drives the accumulated fluid uphole, the chamber is cycled for fluid charging. For the HGP to function properly, the HGP must land in a particular orientation once it reaches depth. Incorrect orientation of the HGP renders the pump inoperable.
In long horizontal wells, the orientation of the pump chamber is random due to the unpredictable and unavoidable rotation and twisting of the production tubing. As a consequence, there is no assurance that the HGP will function correctly when it is landed at its desired location downhole. As far as Applicant is aware, the HGP pump has so far not been practically used for horizontal producers.